Rotary face bit



July 7, 1936. w. J.-MITCHELL ROTARY FACE BIT Filed July 20, 1934 w M 3 m w W I Inventor Attorney Patented July 7, 1936 UNITED STATES ROTARY FACE BIT William J. Mitchell, San Francisco, Calif., as-

signor to Chicago Pneumatic Tool Company, New York, N. Y., a. corporation of New Jersey Application July 20, 1934, Serial No. 130,145

1 Claim.

. My present invention relates to improvements in rotary face bits of the type employed by miners and prospectors and others for obtaining a core or sample of the geological structure of the strata through which the course of the drill is directed for the purpose of determining the actual mining or structural values of the earth or rock through which the drill passes.

My invention is an applied improvement on double-tube drills, i. e. tools wherein an inner tube or core barrel is arranged-concentrically with, but spaced apart from an outer tube or casing, and the core barrel is adapted to receive the core as it is cut by the drill bits. Cutting stones or diamonds are mounted on the drill bit at its working end, and during the drilling operation a stream of water is passed downwardly through passages in the tool to the cutting bits, and some of this water then passes around the face bit and returns upwardly between the exterior of the tool and the wall of the drilled hole. Other portions of the water return upwardly through the core barrel, or inside tube, and thereby assist in floating or lifting the core within the barrel.

In actual practice, the diamonds or cutting stones employed on the drill bits, are comparatively expensive in first cost, as well as costly in the time consumed and labor expended in first setting the cutters, and then in replacing the cutters or diamonds after they have become broken, destroyed, or otherwise rendered inoperative. Repairs and replacements of the bits are also necessary at frequent intervals, because of the wear of the cutting tools, which result in loss of time and heavy expenditures for labor.

In carrying out my invention I provide a drilling tool that eliminates many of the difliculties in present day practice, which tool at the same time is more durable than those now in use with which I am familiar; and the drilling tool of my invention is less expensive in cost and'inrepairs, and requires less time for changing worn parts than is the practice with tools of this character.

The drill is so constructed and fashioned that I am enabled to so direct and guide the tool to insure a true straight hole through the earth, irrespective of the character of the geological structure, and regardless of the depth to which the hole is drilled. By the combination and arrangement of parts at -the working end of the tool the core barrel and easing directly behind or above the bit is protected against most of the wear to which it is usually subjected, and therefore the life of the core barrel and casing is prolonged, and expenses incident to frequent renewals of these tubes are avoided.

In the boring operations I employ one and the same tool for completing the full size hole, in lieu of the usual practice in which two tools are successively employed for this purpose, thereby avoiding the expense, dimculties, and delays incident to present day practices. By the utilization of a set of bits, and interchangeable parts, necessary changes may be made with facility and without material loss of time.

The invention consists in certain novel combinations and arrangements as will hereinafter be more fully set forth and claimed. In the accompanying drawings I have illustrated one complete example of the physical embodiment of my invention, wherein the parts are combined and arranged according to one mode I have thus far devised for the practical application of the principles of my invention. While I have shown one exemplifying structure that is successful in actual practice in carrying out the principles of my invention, it will be understood that changes and alterations may be made therein, within the scope of my claim, without departing from the principles involved.

Figure 1 is a view in elevation of a face bit, one-half in section, showing the embodiment of my invention, and having the cutting stones indicated.

Figure 2 is a view similar to the sectional half of Figure 1 showing a portion of the face-bit with diamonds or cutters omitted.

Figure 3 is a transverseplan view of the face bit showing the water passages at the back side of the bit.

Figure 4 is a vertical sectional view through the face bit.

In order that the general arrangement and relation of parts may be-understood, it is common practice in core drilling to utilize a drill rod comprising an outer sectional drill casing of a.

comparatively heavy durable steel and an inner, sectional core barrel of comparatively. light weight steel tubing, this tubing being spaced within the casing. The passage thus formed is utilized for the transmission of water from the I vanced drill rod section. The bit illustrated in particularly adapted to this type of drilling with a minimum of loss of cutting stones, and a consequent saving of time due to the longer drilling runs that may be made before it is necessary to withdraw the 'tubing and replace the worn face bits. I

In the form of the bit illustrated in the drawing I employ a head I having an integral exteriorly threaded collar 2 by means of which the face bit is threaded into the end of the usual drill rod or drill casing of a drillingmachine. The cutting face 3 of the rotary bit is arcuate or convex shaped and extends fully around the periphery of the tubular head I of the face bit.

In this outer circular arcuate shaped cutting face 3 of the head, I set diamonds or other cutting stones 4, which, when the drill rod and its attached bit are rotated against the stone, ore, or other material being drilled, follows a circular path with the longitudinal center of the drill as the axis of rotation, thus forming a core of the material.

In core drilling operations various conditions in the formation of the strata present serious difilculties to the driller. One of the greatest difficulties arises when cores are being drilled and taken in broken or seamy formations. In this instance the drill'in penetrating one layer, breaks through the further face and is allowed to run free momentarily due to the removal of the natural pressure of the stone being drilled. This allows the drill to speed up and by the time it has traversed the fissure or soft filler between the two strata the bit may be traveling at a greater than practical operating speed. Thus when the face bit is advanced against the newly presented face a tremendous intermittent strain is put upon the settings of the cutting stones and the tendency is to twist or rend the cutters in their settings causing a great loss of stones at this point.

It will be apparent that the utilization of the arcuate shape in the face of the bit provides a greater cutting area allowing a maximum of diamonds to be set thus lessening the amount of cutting any one diamond must perform and thereby lengthening the life of the face bit materially. It is a matter of fact that the number of'diamonds that may be set in this bit face may be as compared with 50 that may be set in the conventional straight faced bit of common usage, and which I have illustrated in U. S. Patent No. 1,907,154, issued May 2, 1933.

Further, the necessity of setting the diamonds sons to overhang on the inner and outer edges of the face of the straight face bit in order to provide the necessary clearances desirable for freely advancing the drill rod and to allow for the free reception of the core, does not lend durability to the straight faced type of bit. It will be apparent that these overhanging cutter stones are subject to the double strain of cutting the rock face, as well as providing the inside and outside clearance. This produces a twisting strain on these inner and outer stones which tends to loosen them in their facets and consequently in creases the footage drilling cost due to lost or broken stones, as well as lost time due to frequent replacements of face bits.

It is further to be remembered that the life of any rotary core drill bit is to be determined by the amount of metal that remains around the stones and forms their secure settings.

By the use of the convex face of my present core bit I overcome these difficulties, and also insure a straighter, truer passage of the drill rod through the rock due to the general guiding eilect produced by the inner and outer slopes of the arcuate face. I

The convex face, besides allowing for a greater number of cutting stones to be set, also allows for these stones to be set in facets at right angles to the convex face over its whole surface. thus insuring that the inner and outer clearance stones are not subjected to the same twisting strain of the same stones of the straight faced bit, as outlined above.

The interior circular core passage 6 of the head I is of the same diameter as the core tubing against which flange 6 abuts, with the exception that at its outmost end it is slightly reduced as at 1. Thus if the clearance stones on the inner slope of the curved face 3 are broken or lost only a comparatively short'distance for friction will be present because as the core passes shoulder 8, clearance is assured.

The water passing to the face bit through the passage between the walls of the outer casing and the inner core barrel enters the face bit through longitudinal holes 9 and oblique holes III which penetrate the inner walls of the core passage 5.

This method of providing passages assures the presentation of water at a point approximately at the very end of the drill rod, and insures the presence of the lubricant (i. e. water) which can then easily flow over and across the cutter stones and back around thedrill rod, or be available to float the core in its backward passage away from the bit.

The angles of the circulating water holes permit water to vent itself at a point approximately one inch closer to the drilling face than has previously been possible with the straight faced bits above referred to and in common universal use.

Reamers or clearance stones may be set at intervals about the head I at a point substantially back from the cutting face 3. These stones insure that the walls of the hole being drilled are properly cleared and reamed to size, thus reducing all exterior friction upon the drill casing and allowing for the steady flow of water in its backward passage around the casing. Having thus fully described my invention, what I claim as new and desire to secure by Letters Patent is: I

A hollow drilling bit having a. central front opening terminating in an interior annular shoulder and an enlarged clearance-bore above said shoulder, said bit having interior discharge ports directly above and in close contiguity to said shoulder, and water-feed passages in the wall of the bit extending upwardly from said ports.

WILLIAM J. m'rcrmm. 

